Top 100 Irish last names explained

IrishCentral has put together a list of the top 100 common Irish surnames.

(O) Nolan - Knowlan Ó Nualláin (nuall, shout): In early times holding hereditary office under the Kings of Leinster, the chief of this sept was known as Prince of the Foherta, i.e. the Barony of Forth, in the present county of Carlow where the name was and still is numerous. A branch migrated to east Connacht and Co. Longford, in Roscommon and Mayo Nolan is used synonymously with Holohan (from the genitive plural); and in Fermanagh as an Anglicized form of ÓhUltacháin (Hultaghan). There was also a sept of the name of Corca Laoidhe which is now well represented in Co. Kerry.

Prendergast - de Priondragás: One of the powerful families which came to Ireland at the time of the Anglo-Norman invasion. They are still found mainly in the places of their original settlement. Some of those in Mayo assumed the name FitzMaurice.

MacQuaid - Quade  Mac Uaid (son of Wat): A well-known name in Co. Monaghan and adjacent areas. Without the prefix Mac the name is found in Co. Limerick.

(O) Rafferty - Ó Raithbheartaigh, mod. Ó Raifeartaigh: Though etymologically this (from rath bheartach, prosperity wielder) is distinct from Ó Robhartaigh (from robharta, full tide) anglicized O’Roarty, these two names have been treated as one, at least since the fifteenth century. As co-arbs of St. Columcille on Tory Island Roarty is now mainly Co. Donegal while Rafferty is of Co. Tyrone and Co. Lough.

(O) Rahilly - Ó Raithile: this well-known Munster family originated as a branch of the Cenél Eoghain in Ulster buthas long been closely associated with west Munster, the poet Egan O’Rahilly for example was a Kerryman.

Redmond - Réamonn:  
A Hiberno-Norman family of importance throughout Irish history. They are associated almost entirely with South Wexford. The branch of the MacMurroughs in north of that county, some of whom adopted the name of Redmond whose chief was called Mac Davymore, are quite distinct from the MacRedmonds.

(O) Regan - Ó Riagain: Ó Réagainis used in county Waterford. There are three septs with this name. That shown as of Leix was in the early times one of the ‘Tribes of Tara’. The eponymous ancestors of the Thomond sept were akin to Brian Boru. The third was akin to the MacCarthys.

(O) Reilly - Ó Raghailligh: One of the most numerous names in Ireland, especially so in Co. Cavan. The prefix O has been widely resumed in the anglicized form. The head of this important sept was chief Breffny O’Reilly

(O) Riordan - Rearden Ó Riordáin: This numerous sept belongs exclusively to Minster, he earlier form of Ó Rioghbhardáin reveals its derivation from riogh bhard, royal bard.

(O) Rooney - Ó Ruanaidh: Originating in Co. Down, where Ballyroney locates them, this name is now numerous in all the provinces except Munster. In West Ulster and north Connacht Rooney is often an abbreviation of Mulrooney.

(O) Shea - Shee  Ó Séaghdha; mod. Ó Sé (séaghdha, hawklike, secondary meaning stately): Primarily a Kerry sept, but (as in Shee) it is notable as the only Gaelic-Irish name among “the Tribes of Kilkenny’ to which county and Co. Tipperary a branch of the sept migrated in the thirteenth century.

(O) Sheehan - Sheahan Ó Síodhacháin: (The obvious derivation from síodhach, peaceful, is not accepted by some Celtic scholars). The Dalcassian sept which spread southwards accounts for the majority of Sheehans who are now very numerous in Co.s Cork, Kerry, and Limerick. Formerly also there was an Uí Maine sept of this name which, however, is rarely found in Connacht today.

(O) Slattery - Ó Slatara, Ó Slatraigh (slatra, strong): Of Ballyslatterly in east Clare. The name has now spread to adjacent counties of Munster.

Smith - Smyth  When not the name of an English settler family, Smith is usually a synonym of MacGowan, nearly always so in Co. Cavan.

(Mac) Spillan(e) -  Mac Spealáin (derivation as O’Spillane): The family is, however, quite distinct from Ó   Spealáin (O’Spillane) Spollan and Spollin, rarely retaining the prefix Mac, are numerous in County Offaly. Older anglicized forms were Spalane and Spalon.

(O) Sullivan - Ó Súileabhain: (While there is no doubt that the basic word is súil (eye) there is a disagreement as to the meaning of the last part of the name). This is the most numerous surname in Munster and is third in all of Ireland. Originally of south Tipperary, the O’Sullivans were forced westwards by the Anglo-Norman invasion where they became one of the leading septs of the Munster Eoghanacht. There were several sub-septs, of which O’Sullican Mor and O’Sullivan Baere were the most important.

(Mac) Sweeney - Swiney  Mac Suibhne: (the word suibhne denotes peasant, the opposite of diubhneI). Of all galloglass origin it was not until the fourteenth century that the three great Tirconnell septs of MaSweeney were established; more than a century later a branch went to Munster.